Related subject matter is disclosed in the concurrently filed application entitled xe2x80x9cA BROADBAND ELECTRONIC Nxc3x97N CROSS-CONNECT SWITCH USING TUNABLE LASERS by the inventors, C. R. Doerr, C. P. Dragone, I. P. Kaminow and A. M. Glass, both applications being assigned to the same Assignee.
The present invention relates to a multiple wavelength laser and, more particularly, to a multiple wavelength laser configuration characterized by N=NaNb output wavelengths selected using only Na+Nb control signals.
Wavelength division multiplexing (WDM) allows high transmission capacity by allowing many wavelengths to be simultaneously transmitted in each fiber. An important device that is needed at each WDM node is a broadband cross-connect switch for providing complete connectivity between incoming and outgoing fibers. Such a cross-connect switch can be realized by combining a waveguide grating router with a set of tunable lasers. A tunable lasers can be simply realized by using an Nxc3x971 router as described in the article xe2x80x9cChromatic focal plane displacement in parabolic chirped waveguide grating routerxe2x80x9d by C. Doerr et al, published in IEEE Photon. Technol. Lerr., vol. 9, pp. 627-635, May 1997. However, in such an arrangement N controls are needed and such laser may be difficult to realize in integrated form for large N. A tunable laser having a reduced number of controls is described in the article entitled xe2x80x9cArrayed-Waveguide grating lasers and their applications to tuning-free wavelength routingxe2x80x9d by Y. Tachikawa et al, IEE Proc. -Optoelectron., Vol 143, No. 5, pp. 322-328, October 1996. However, the article does not describe a practical way to integrate a single output tunable laser.
Therefore, there is a continuing need for an integrated single output tunable laser having a reduced number of wavelength selection controls.
In accordance with the present invention, we disclose an integrated, single output port, tunable multiple wavelength laser having N=NaNb output wavelengths selected using only Na+Nb control signals. Each of Nb ports can output Na of the laser wavelengths, the port being selected by the Nb control signals and the particular one of the Na wavelengths being selected by the Na control signal. An Nbxc3x971 router combines the signals from the Nb output ports into a single output.
In another embodiment, the laser apparatus comprises a waveguide grating router including a first and second free-space regions connected by a plurality of waveguide arms having a quadratic path length variation. The input side of the first free-space region includes Na input waveguides each separated by a spacing xe2x80x9caxe2x80x9d and each including a reflective termination which is controlled by a separate one of a first group of control signals, 1xe2x88x92Na. The output side of the second free-space region includes Nb output waveguides each separated by a spacing xe2x80x9cbxe2x80x9d, where xe2x80x9caxe2x80x9d is equal to Nb times xe2x80x9cbxe2x80x9d, each output waveguide including a reflective termination which is controlled by a separate one of a second group of control signals, 1xe2x88x92Nb, each reflective termination being partially transmitting and connected as a different one of the Nb output ports of the laser. In yet another embodiment, the laser is connected to a Nbxc3x971 router that combines the Nb outputs from the laser into a single output.